1. Field of the Invention
The invention relates in general to elevator systems, and more specifically, to new and improved methods and apparatus for determining and maintaining the advanced car position of an elevator car.
2. Description of the Prior Art
In relatively low speed elevator systems, such as under 500 fpm, it is common to utilize indicia in the hatchway which cooperate with electrical switches mounted on the car. The indicia serve as switch actuators when the elevator car passes the various indicia. Examples of such switch/actuator arrangements include (a) an arrangement for producing a light beam which is interrupted by an actuator, (b) mechanical switches with cam followers which are operated by a cam actuator, (c) a magnetic switch in the form of an inductor relay, with the inductor relay having an incomplete magnetic circuit which is completed by an actuator in the form of a plate or vane constructed of magnetic material, (close proximity of the magnetic switch and vane completes the magnetic circuit to operate the switch) and, (d) magnetic switches, such as reed switches, which are operated from one position to another position while being subjected to a magnetic field, such as from a permanent magnet actuator.
U.S. Pat. No. 3,856,116 illustrates a cam/switch arrangement, U.S. Pat. No. 3,889,231 illustrates a magnet/switch arrangement, and application Ser. No. 171,788, filed July 24, 1980, now U.S. Pat. No. 4,322,703, discloses a magnetic plate/switch arrangement, all of which are assigned to the same assignee as the present application.
The usual control functions provided by these switch/actuator arrangements include (a) detection of the arrival of the elevator car at a point relative to a target floor where slowdown should be initiated, (b) detection of the arrival of the elevator car at a point relative to the target floor where stopping should be initiated, and (c) detection of the car passing locations relative to the floors where the advanced car position AVP is incremented, or decremented, depending upon car travel direction. These actuators for implementing these functions are normally disposed in five vertical lanes in the hatchway. For example, function (a) requires one vertical lane, such as for mounting landing cams, which are also used for releveling, function (b) requires two vertical lanes for establishing slowdown distances relative to the floor, for each travel direction from which the floor can be approached, and function (c) requires two vertical lanes for alternately notching the floor selector from two switches, to prevent contact bounce from falsely notching or changing the advanced car position. U.S. Pat. No. 3,902,572, which is assigned to the same assignee as the present application, describes these functions in detail. The advanced car position is defined as the floor at which the stationary car is sitting, and the closest floor to the moving car at which the car can make a normal stop.
Each vertical lane of indicia in the hoistway adds substantially to the initial cost, as well as to the maintenance costs, of an elevator system, and thus it would be desirable to reduce the number of vertical lanes of indicia, and their associated switches, if such the reduction can be accomplished without loss of function.